This invention relates to the recovery and reutilization of surfactants from fluids that are produced as a result of enhanced oil recovery operations. More particularly, the invention employs temperature cycling to extract surfactants first into an oleic phase, and then into an aqueous phase.
Surfactants flooding has become one of the more promising enhanced oil recovery techniques for recovering oil after waterflooding. Generally, the method of surfactant flooding employs the injection of a surfactant in an aqueous solution or emulsion to sweep through the formation and recover oil. This may be followed by a polymer solution for mobility control and improved sweep efficiency. It is believed that surfactants are effective because of their ability to reduce the interfacial tension between crude oil and water. This reduction of interfacial tension permits the creation of various oil, water and surfactant emulsions in the formation. Thus, produced fluids comprise one or more oil, water and surfactant emulsions, and oil and brine which may or may not contain surfactant.
Because of the relative amounts of oil and water produced in chemical flooding, produced emulsions are frequently oil-in-water emulsions. Upon settling, the composition of the produced fluids may change to different types of emulsions, as well as separate oil and water phases containing different amounts of surfactants. Numerous methods have been devised to break water-in-oil emulsions, oil-in-water-emulsions, and to aid in phase separation of produced fluids.
Two methods of recovering surfactants from produced emulsions of oil, water and surfactant are disclosed in U.S. Pat. Nos. 4,516,635 and 4,559,148. U.S. Pat. No. 4,516,635 employs a two-step extraction process with a first extracting compound selected from the group of alkali metal salts and ammonium salts of various alkylbenzene sulfonates to form three phases, a crude oil phase, a first middle phase and an aqueous phase. The second extraction step mixes an alkanol having 2 to 4 carbon atoms with the first middle phase to form three additional phases, including a surfactant rich, second middle phase.
U.S. Pat. No. 4,559,148 discloses mixing a produced emulsion with an alkali metal chloride salt and butanol or pentanol and allowing the fluids to separate into two phases, an oleic phase and an aqueous phase. The oleic phase is mixed with fresh water containing about 1% to about 10% by weight of isopropanol, ethanol or methanol, and the mixture is allowed to separate into at least two phases, a substantially water-free and surfactant-free crude oil phase and an aqueous phase containing virtually all of the surfactants originally within the produced emulsion.
U.S. Pat. No. 4,277,352 teaches the addition of anionic or nonionic solubilizers including alkoxylated alkylphenols to produced emulsions to shift the enhanced oil recovery surfactants from emulsions into aqueous solutions.
Other emulsion breaking processes are disclosed in U.S. Pat. Nos. 3,637,521; 3,687,845; 4,029,570; 4,073,344; 4,216,079; and 4,261,812. This is not an exhaustive list.